Flotation machines

ABSTRACT

699,045. Froth-flotation apparatus; impellers. BOLIDENS GRUVAKTIEBOLAG. Aug. 2, 1951 [Aug. 2, 1950], No. 18337/51. Classes 82(ii) and 86 A mixing impeller for a froth flotation machine comprises a disc 3, to the upper side of which radial blades s 4 are secured, and a guide baffle device surrounding t h e blades, there being a peripheral recess 5 in the disc between each blade which is deepest adjacent the blade trailing edge. Each baffle 9 of the baffle device is at a small angle &#34;a&#34; to the radius of the impeller. Smaller radial blades 10 are fitted beneath the disc 3.

June 2 1955 P. G. KIHLSTEDTY LEIAL 2,711,823

FLOTATION MACHINES Filed Aug. 2, 1951 2 Sheets-Sheet l J1me 1955 P. G. KIHLSTEDT ETAL 2,711,823

FLOTATION MACHINES I 2 Sheets-Sheet 2 Filed Aug. 2, 1951 E NVENTORS W 1m 1M FLOTATION MACHINES Per Gudmar Kihlstedt, Boliden, and Tore Rudolf Liifgren,

Dala-Finnhyttan, Sweden, assignors to Bolidens Gruvaktiebolag, Skelleftehamn, Sweden, a joint-stock company limited of Sweden Application August 2, 1951, Serial No. 239,878

Claims priority, application Sweden August 2, 1950 4 (Ilaims. (Cl. 209-469) This invention relates to a flotation machine for the flotation of ore bearing pulp, and particularly a machine of the subaeration type having a mechanical air distributor or agitator for froth flotation.

For carrying out froth flotation air is introduced into a cell containing an aqueous suspension of finely divided particles of the ore. The air then rises through the suspension in form of bubbles and forms a froth blanket on the surface of the liquid. The cell is usually provided with an impeller for aerating and agitating the liquid, for which purpose the impeller has a plurality of blades.

It is known to arrange said impeller in such a way that its blades extend outside its disc to form a so called receded disc. However, this will cause uncontrollable movements of the pulp outwardly to which pulp air has been added.

It is also known to use rods or vertically arranged plates around the impeller to further divide the air bubbles of the pulp. To counteract the rotation of the pulp also radial walls within the Zone above the impeller have been proposed. Such walls however tend to accumulate the air bubbles and so to cause an air distribution in the pulp which is not uniform.

The present invention has now for its object a flotation machine by which said disadvantages are avoided, the pulp being controllably guided outwardly against stationary guide blades or bafiles, and which machine presents also further improvements which will be understood by the following detailed description of a preferred embodiment of the novel machine.

The description is given under reference to the accompanying drawings in which:

Figure 1 is a diagrammatic vertical section of a machine according to a preferred embodiment of the invention;

Figure 2 is a horizontal section of the machine shown in Figure 1 taken on line A-A;

Figure 3 is a detailed fragmentary vertical view of the impeller included in the machine of Figures 1 and 2; and

Figure 4 is a horizontal section of the impeller of Figure 3, taken on line C-C of said figure.

In the drawings 1 is a trough or cell which is shown made of metal sheet but which also may be made of wood or any other suitable material. The top portion of the cell has a rectangular horizontal transverse section to enable it to be directly connected to an adjacent cell. Below the line B--B of Figure l the horizontal section is substantially circular instead of rectangular. Said intermediate portion of the cell has the shape of a frustum of a cone with a slightly inclined wall. The lowest portion of the cell below the impeller also forms a frustum of a cone but the wall of this cone is much more inclined than the abovementioned cone as shown by Figure l.

The cell 1 has an opening 2 at one side for introducing pulp to be treated into the cell. The opening may be rectangular as shown or it may have any other States Patent 2,711,823 Patented June 28, 1955 suitable form. It is located on a level just below the lower surface of the froth blanket formed when operating the machine. At the bottom or near the bottom the cell 1 has another opening 3 for withdrawing the tailing. Also this opening may be rectangular or have any other form. 4 is a suitable rotating means for skimming off the concentrates.

Centrally in relation to the said intermediate and lowermost portions of the cell 1 an air agitating means is provided, the impeller or rotor of which is generally designated by 5 in Figure l. 6 designates generally stationary guide blades or baffles mounted on the pipe 8 which surrounds the impeller spindle (not shown in Figure I). Said spindle and the impeller are driven from a suitable source such as an electric motor (not shown) over the pulley 9 shown at the upper end of the spindle. 7 is an opening in the pipe 8 for admitting air to the impeller.

Referring now to Figures 3 and 4 which show the impeller more in detail 11 is a hub mounted on the spindle 12 to rotate therewith. Integral with the hub 11 or secured thereto is a disc 13, on the upper side of which is radially mounted a number of blades 14. The disc 13 has a peripheral recess 1'5 between each blade, each recess being deepest adjacent to the trailing side of each blade. The direction of rotation is shown by the arrow in Figure 4. The purpose of said recesses is to facilitate the passage of the pulp into the impeller. Between the pipe 8 mentioned above and the spindle 12 there is a space 16 to enable air to pass into the impeller. To the underside of the disc 13 of the impeller there is secured a number of radial blades 20 of a low height.

To the pipe 8 a plate 17 is secured in a suitable way to cover the impeller. On said plate 17 an annular member 18 is mounted which is provided with a number of guide blades or bafiles 19, the direction of each blade 19 constituting a small angle a with the radius.

When in operation the impeller is rotated by its spindle 12, due to centrifugal action of the blades 14 of the disc 13 air will be forced into the space 16 and then between the hub 12 and the plate 17. To obtain the amount of air required an air compressor may be connected to the space 16. The pulp enters the cell through the opening 2 (Figure l). The blades 20 serve to maintain the pulp in suspension. When the impeller is rotating a vacuum is created in a known manner at the trailing sides of the blades 14 causing the pulp to be drawn in through the recesses 15 of the disc 13 and to be mixed with air drawn into the impeller from the space 16. The mixture of pulp and air is impelled against the next blade 14 of the impeller so that the air will be finely divided. Then the air-pulp mixture will be thrown outwardly from the impeller and forced to pass between the stationary guide blades or batfies 19. Said blades will further divide the air bubbles formed. Due to the fact that the guide blades 19 make an angle a with the' radius against the direction of rotation of the impeller (Figure 4) the rotation of pulp, caused by the impeller, will be substantially compensated and the pulp will leave the guide blades 19 in radial directions substantially. This will give a uniform air distribution throughout the whole area of the cell which improves the flotation process extraordinarily.

Due to the recesses 15 of the disc 13 the pulp will be taken from a zone substantially free from air bubbles below the impeller. By this the pulp mixed with air and appearing above and around the impeller .will not be drawn in into the impeller.

When the air bubbles with attached concentrate mineral particles rise to the surface a froth blanket is formed in the upper zone of the cell and the froth is withdrawn by the rotating means 4 or overflows the sides of the cell. The pulp to be treated is introduced through the opening 2' which is located beneath said froth blanket. Therefore the mineral particles of the entering pulp which are to-beflotatedwill attach to, the rising air bubbios and be carried to the surface. In such away the pulp will have less such particles to. be ilotated nearer the bottom of the flotation cell. In. the conventional flotation machines the pulp usually is, ledv through a pipe or the like directly into the centre of theimpeller so that all pulp has to pass the impeller. Therefore the. pulp in the bottom Zone of such machines will usually be relatively rich in the mineral particles which are to be flotated and there is a risk of. the pulp thrown outwardly from the impeller flowing directly through the outlet of the machine. In the machine of theinvention, however, the pulp leaving the machine will. contain a minimum of the particles to be fiotated.

As will be understood the pulp leaving the machine through the opening 3 will be passed to the next cell of the series of cells or bediscarded.

Due to the fact that the lower portion of the cell has a circular transverse section, no corners exists which would interfere with the flow conditions and so with the air distribution.

According to the invention the distance between the under surface of the impeller 5 and the bottom of the cell 1 should be within the range of /2 to /s of the diameter of the impeller. This involves a greater distance than is usual, but it will enable the pulp in said zone to be freed from any air bubbles before leaving the cell through the outlet 3. bottom of the cell.

While various specific examples of preferred methods embodying the present invention have been described above, it will be apparent that many changes and modi: fications may be made in the apparatus herein described without departing from the spirit of the invention. It is therefore to be understood that the particular apparatus set forth above are intended to be illustrative only and are not intended to limit the scope of the invention as defined in the following claims.

Having now particularly described and ascertained the nature of our said invention and in which manner the same is to be performed, we declare that what we claim is:

l. Flotation machine comprising a cell for containing the pulp being treated, means for aerating said pulp, said aerating means comprising a rotatable impeller having a disc and radially directed blades thereon, each blade having substantially a uniform height along the radius of the disc, the periphery of the said impeller disc being formed with recesses between the blades to permit pulp to be drawn upwardly from. the section of the cell below said impeller d sc, an upper stationary disc positioned immediately above said blades, said aerating means being located in the lower section of said cell to form a rising 5 column of air bubbles in the cell to form a froth blanket in the upper section of said cell, the lower section of said cell below the level of the under surface of said means for aerating the pulp having the form of a frustum of a cone, means for forcing air into the space between the rotatable impeller and said stationary disc, thereby supplying air to said aerating means, means for introducing pulp to be treated into the cell and located on a level just below the lower surface of said froth blanket, means for Withdrawing concentrates from the cell and means for withdrawingtailings from the cell.

2. Flotation machine comprising a cell for containing pulp being treated, means for aerating said pulp, said aerating means comprising a rotatable impeller having a disc and radially directed blades thereon, each blade having substantially a uniform height along the radius of the disc, the periphery of the said impeller disc being formed with recesses between the blades to permit pulp to be drawn upwardly from the section of the cell below said impeller disc, an upper stationary disc positioned imme- It will also reduce the wear of the diately' above said blades, saidaerating means being located in the lower section of said cell to form a rising column of air bubbles in the cell to form a froth blanket in the upper section of said cell, means for forcing air into the space between the rotatable impeller and said stationary disc, thereby supplying air to said aerating means, means for introducing pulp to be treated into the cell and located on alevel just below the lower surface of said froth blanket, means for Withdrawing concentrates from the cell, and means for withdrawing tailings from the cell, said last-mentioned means comprising an opening in-the wall of'the cell, the opening being substantially below the level of the under surface of said means for aerating the pulp.

3. Flotation machine comprising a cell for containing the pulp being treated, means for aerating said pulp, said aerating means comprising a rotatable impeller having a disc and radially directed blades thereon, each blade having substantially a uniform height along the radius of the disc, the periphery of the said impeller disc being formed with recesses between the blades to permit pulp to be drawn upwardly from the section of the cell below said impeller disc, an upper stationary disc positioned immediately above said blades, said aerating means being located in the lower section of said cell to form a rising column of air bubbles in the cell to form a froth blanketv in the upper section of said cell, said aerating means also including a substantially circular set of deflector baffies positioned about butspaced from the periphery of said blades, the alignment of each baflie forming an angle from the radius of said disc to substantially eliminate the swirling movement of pulp leaving the impeller, means for forcing air into the space between said rotatable impeller and said stationary disc, thereby supplying air to said aerating means, means for introducing pulp to be treated into the cell and located on a level just below the lower surface of said froth blanket, means for Withdrawing concentrates from the cell and means for withdrawing tailings from the cell.

4. Flotation machine comprising a cell for containing the pulp being treated, means for aerating said pulp, said aerating means comprising a rotatable impeller having a disc and radially directed blades thereon, each blade having substantially a uniform, height along the radius of the disc, theperiphery of the said impeller disc being formed with recesses between the blades to permit pulp to be drawn upwardly from. the sectionv of the cell below said impeller disc, each. of said recesses in said disc between said blades has its greatest depth adjacent the trailing edge of each blade, an upper stationary disc positioned immediately above said blades, said aerating means. being located in the lower section of said cell to form a rising column of air bubbles in the cell to form a froth blanket in the upper section of said cell, means for forcing air into the space between said rotatable impeller and said stationary disc, thereby supplying air to said aerating. means, means for introducing pulp to be treated into the cell and located on a level just below the lower surface of said froth blanket, means for withdrawing concentrates from the cell and means for withdrawing tailings from the cell.

References Cited in the file of this patent UNITED STATES PATENTS 1,417,895 Fahrenwald May 30, 1922 1,445,042 Ruth Feb. 13, 1923 2,031,590 Daman Feb. 25, 1936 2,134,410 Kraut Oct. 25, 1938 2,243,309 Daman et al. May 27, 1941 2,274,401 Dromgold Feb. 24, 1942 2,436,375 Booth Feb. 24, 1948 2,609,097 Deving Sept. 2, 1952 FOREIGN PATENTS 108,227 Australia Aug. 8, 1939 445,547 Great Britain Oct. 22, 1936 

1. FLOTATION MACHINE COMPRISING A CELL FOR CONTAINING THE PULP BEING TREATED, MEANS FOR AERATING SAID PULP, SAID AERATING MEANS COMPRISING A ROTATABLE IMPELLER HAVING A DISC AND RADIALLY DIRECTED BLADES THEREON, EACH BLADE HAVING SUBSTANTIALLY A UNIFORM HEIGHT ALONG THE RADIUS OF THE DISC, THE PERIPHERY OF THE SAID IMPELLER DISC BEING FORMED WITH RECESSES BETWEEN THE BLADES TO PERMIT PULP TO BE DRAWN UPWARDLY FROM THE SECTION OF THE CELL BELOW SAID IMPELLER DISC, AN UPPER STATIONARY DISC POSITIONED IMMEDIATELY ABOVE SAID BLADES, SAID AERATING MEANS BEING LOCATED IN THE LOWER SECTION OF SAID CELL TO FORM A RISING COLUMN OF AIR BUBBLES IN THE CELL TO FORM A FRONTH BLANKET IN THE UPPER SECTION OF SAID CELL, THE LOWER SECTION OF SAID CELL BELOW THE LEVEL OF THE UNDER SURFACE OF SAID MEANS FOR AERATING THE PULP HAVING THE FORM OF A FRUSTUM OF A CONE, MEANS FOR FORCING AIR INTO THE SPACE BETWEEN THE ROTATABLE IMPELLER AND SAID STATIONARY DISC, THEREBY SUPPLYING AIR TO SAID AERATING MEANS, MEANS FOR INTRODUCING PULP TO BE TREATED INTO THE CELL AND LOCATED ON A LEVEL JUST BELOW THE LOWER SURFACE OF SAID FROTH BLANKET, MEANS FOR WITHDRAWING CONCENTRATES FROM THE CELL AND MEANS FOR WITHDRAWING TAILINGS FROM THE CELL. 